1. Field of the Invention
The subject disclosure relates to paper-based container lids and methods of making the same, and more particularly to lids for containers, such as beverage cups, which can be economically formed, are capable of being used with hot liquids, and include a sealing channel that creates an enhanced sealing interface with a corresponding rim formed on the container.
2. Background of the Related Art
Hot beverages, such as coffee, tea or the like, are frequently sold as a takeout item and supplied in disposable cups with thin plastic lids fasten over the rim of drinking cups. Such lids prevent spillage and evaporation of the beverage within the cup, and help insulating the contents of the cup from the ambient temperature by closing the cup opening. Drinking cup lids, such as those used by restaurants, convenience stores, and coffee houses, are commonly made of plastics. They are inexpensive and therefore suitable for disposable use. A well-known method of manufacturing plastic cup lids is by vacuum forming, which is a plastic thermoforming process that involves forming thermoplastic sheets into three-dimensional shapes through the application of heat and pressure. During the vacuum forming process, the plastic material is heated until it becomes pliable, then placed over a mold and drawn in by a vacuum until it takes on the desired shape. The vacuum thermoforming allows cup lids to be manufactured very inexpensively.
U.S. Pat. No. 4,589,569 discloses a disposable lid of one piece plastic construction that can be manufactured relatively inexpensively. The lid is manufactured by a thermoforming operation, preferably vacuum forming. The lid includes an annular mounting portion for engaging the lip of the cup; an annular side wall extending upwardly from the mounting portion; and a top wall having a drinking opening and a recess formed adjacent the drinking opening to accommodate the upper lip of the user.
Some plastics are not biodegradable, and increasing environmental concerns drive the needs for inexpensive and biodegradable lids as alternatives for disposable plastic lids.
Efforts to produce paper-based lids for containers/cups have had limited commercial success due to the complicated manufacturing process and the poor sealing between the cup body and the lid sealing ring that results in leakage of fluid contents from the cup. The poor lid sealing and leakage is worse when the cup is for hot beverages. Lids made from a single paperboard blank do not effectively seal around the rim of the containers. During the manufacturing process, substantial crimps are formed in the sealing ring portion of the lid, resulting in gaps when the ring attaches to the rim of the container and consequently a source of fluid leaks.
U.S. Publication No. 2010/0243722 addresses the leaking problem by using paperboard lids manufactured without the substantial crimps formed in the sealing rings. The lid includes a single contiguous molded paperboard body configured to conformingly couple to the container rim. The lid is formed by placing an unformed paperboard blank inside a press machine that uses compression forces to shape the paperboard blank into the lid. The draw and pressure rings hold the blank in place, while the male and female mold components of the machine compress the blank into a lid shape. By holding the paperboard blank with draw and pressure rings while the blank is pressed into the lid shape, the formation of substantial crimps typically occurring during the press step can be prevented.
There have been reports of paper-based cups with integrated lids. For example, U.S. Pat. No. 6,592,504 discloses a disposable paperboard cup that includes a bottom insert, and a substantially truncated conical body with an integral lid and a cup opening. The integral lid is movable between a raised position and a closed position. The lid has a free edge with an opening that provides an access to the fluid contents inside the cup when the lid is in the closed position. The lid is formed from a semi-circular die-cut piece adjoined to the body portion of the cup. The cup with integrated lid requires complex folding mechanisms, rendering it expensive and difficult to manufacture. Furthermore, the cup with integrated lid possesses a wide top, which is subjected to spillage and is difficult to achieve an adequate sealing between the lid and the container body, resulting in leaking of the packaged contents.
Moreover, Inmaco BV located in the Netherlands offers for sale a paper-based cup lid. A cross-section of the cup-lid interface in the Inmaco product is illustrated in FIG. 13E. As shown therein, the Inmaco lid 80 includes a cylindrical sidewall 82 and a top wall 81. The sidewall 82 is spiral wound and is made out of 3 layers of paperboard and adhesive and includes a circumferentially formed bead 85 which extends radially inward from the sidewall 82. When the lid 80 is placed on top of the rim “R” of the cup, the sidewall 82 deflects so that the rim “R” of the cup can pass by the circumferential bead 85. Once past the bead 85, the sidewall 82 relaxes and traps the rim “R” of the cup between the bead 85, a flat section 87 of the sidewall 82 and the top wall 81.
As noted above, the bead 85 formed in the sidewall 82 around the circumference of the Inmaco lid 80 secures the lid to an appropriately sized container. The fit is fairly tight radially, i.e. there is a close match between the outer diameter of the container rim “R” and the inner diameter of the lid 80. However, there is not a tight fit axially; the lid 80 can move up and down and thus it does not provide good leak resistance for liquids. In fact, in the lids tested by the inventors, the lid could move up and down by as much as 1.5 mm. Moreover, since the sidewall 82 of the lid in the sealing zone is flat (section 87) and rim “R” is curved there is no mating contact between the sidewall 82 and rim surfaces, and thus the seal is poor.
A further disadvantage of the Inmaco lid 80 is that the sidewall has a spiral seam. It is difficult to minimize the visual impact this seam by compressing it further, because this won't necessarily make the gap between the ends of the sidewall blank smaller. Moreover, using a spiral wound sidewall makes it extremely difficult to register or position the seam at a specific location around the periphery of the lids. For these reasons and to the best knowledge of the inventors, the Inmaco lid has not been offered commercially with a hole for drinking nor has it been used with liquids.
An additional disadvantage of the Inmaco lid 80 is its stacking height. Because the sidewall of the Inmaco lid 80 is substantially straight, with no taper, and the bead 85 is formed radially inward, the stacking height of the Inmaco lid 80 is limited by the location of the bead 85 and the height of the skirt below the bead.
It is known that a bead or fill line in a beverage container such as a paper cup can be formed by utilizing a spinning forming disc, wherein the disc is spun into a position near the top of the sidewall of the paper container thereby creating a bead, groove or fill line in the sidewall of the container. This apparatus requires a cam follower in a machined cam track, a cam drive shaft in a relatively complicated header assembly, and an auxiliary loader for the spinning disc. Thus, a substantial number of precision moving parts are required. Such units are therefore relatively expensive to construct and to maintain.
To address these drawbacks, U.S. Pat. No. 4,247,277 disclosed a non-spinning apparatus for forming a fill line or groove in paper cups or containers by axially compressing an annulus of a resilient material into the inside of paper cups, thereby causing a controlled deformation of the cup material outwardly about its periphery. Rather than a rotating movement of the spinning disc, the apparatus relies on the up- and down-movement of the compressed resilient material for a formation of the fill line or groove. The outward deformation occurs internally of a cup die where a portion of the sidewall of a paper cup or container confined within the die is forced by the compressed annulus to form the fill line or groove. While this apparatus is less complicated than the spinning forming discs previously used for the same purpose, it is still a complicated apparatus which requires moving parts that tend to wear, require maintenance and replacement.
U.S. Pat. No. 5,637,332 discloses a simplified apparatus for forming a fill line in a paper container such as a paper cup that includes no moving parts. A fill line is formed by forcing a punch of a mating ring into a finished cup positioned in a die which includes an annular recess spaced below the rim of the finished cup, and the annular recess terminates in a bottom edge to serve as an anvil surface for forming the fill line.
U.S. Pat. No. 6,663,926 discloses an apparatus for forming a rib on the side wall of the cup via an operation of the rib processing tool performed outside the cup body, thereby improving the process efficiency by eliminating a need of moving a rib processing tool in and out against the cup body. Furthermore, the apparatus allows the rib to be formed gradually in the circumferential direction of the cup body, in accordance with the relative rotation between the cup body and the rib processing tool. Therefore, it is possible to reduce force added to the cup body during the rib formation in comparison with the case in which the entire rib is formed at once.
U.S. Pat. No. 7,753,832 discloses an apparatus for molding an article produced from paperboard or cardboard, wherein a momentary irradiation of the microwave frequency is exerted on the molded board to improve its moldability. To form a cup with an annular crease on the side wall, the cup is placed on a base and supported at its side wall by a carrier ring having an annular groove that is corresponding to the crease to be made in the cup. The apparatus includes a base to support the cup bottom; a carrier ring with an annular groove to support the cup side wall; a moving tool; a crease forming tool connected to the moving tool, wherein the crease forming tool is corresponding to the groove of the carrier ring and the crease to be created on the cup side wall. The moving tool is lowered inside the cup so that its lower end is level with the groove of the carrier ring, and the irradiators on the moving tool exert microwave frequency on the side of the cup at the point where the crease is to be formed to permanently mold the creased side wall.
Despite extensive research for paper-based container lids, particularly for the drinking cup lids, several drawbacks remain. Examples of such drawbacks described in part above include: complexity of production; lack of recyclability either due to the use of recyclable/compostable materials or the difficulties in operating reclamation systems when the cup and the lid are made of different materials; insufficient consumer acceptance due to inadequacies in material “mouth feel” or design, decreased aesthetic appeals when the packaged fluids stain the lid manufactured from molded pulp; and poor lid performance due to inadequate sealing of the lid to the cup, especially after several usage cycles.
Accordingly, there is still a need for paper-based container lids that can be produced economically and with less complicated processes than known paper-based lids, and which provide acceptable lid performance (if not enhanced) compared to known paper-based lids. Moreover, there is a need for paper-based container lids which can be used with hot liquids and are constructed to provide an enhanced sealing interface with the containers so as to minimize, if not eliminate, the leakage of contents packaged in the containers.